Hydrocarbon containing fluids such as gasoline are the most common power source for internal combustion engines. Gasoline must be carried by the vehicle, usually in a fuel tank. The fuel tank is located at some convenient location within the structure of the vehicle. Often the fuel tank is contained within a reinforced area so as to provide crash protection for the fuel tank.
In order to provide a convenient access to the tank, the vehicle is typically fitted with a fuel filler inlet. Thus, there is required a conduit to extend between the fuel filler inlet and the tank. That conduct may be long or short and may be of convoluted configuration depending upon the relative location of the tank and the filler inlet.
Most hydrocarbon containing fuels are relatively volatile. Accordingly, the fuel filler conduit must contain at least one layer to substantially inhibit, if not totally prevent, passage of vapours from the liquid fuel to ambient atmosphere outside the filler pipe.
Previously fuel tanks and fuel filler pipes have been made of metal. However, for cost and other reasons, more recently fuel tanks have been manufactured of plastic materials. Fuel tanks being relatively large hollow structures are particularly suited to be made in blow molding procedures. With the advent of plastic rather than metallic fuel tanks, it is now desirable to use plastic fuel filler pipes.
It is well understood by those familiar with the handling and storage of fuels such as gasoline, that static electricity can be generated during the filling procedure. Static electricity in fuel storage systems is dependent primarily on the rate of fill, the amount of turbulence in the fuel as it passes along the conduit and the amount of charge present in the fuel before contacting the vehicle. As fuel is passed along the conduit there is a good likelihood that a static electricity charge will build up. If that charge is permitted to increase until a spark is generated there is a danger of explosion of fuel vapours. Such explosions can be catastrophic not only to the fuel system but the entire vehicle and those in the vicinity of the vehicle.
In the past when fuel tanks were manufactured from metals and fuel filler pipes were also metallic, the natural conductivity of the metal served to bleed off any static electricity as it was generated thus preventing an increase in charge to the point where there was a spark.
In almost all systems, the part of the filler head which touches the refuelling nozzle is made of a conductive material and that is connected directly to the vehicle ground. This effectively prevents a difference in electrical potential between the refuelling nozzle and the filler head and the vehicle. Thus, there is no spark discharge. However, when a plastic fuel filler pipe is desired, because of the normal insulative value of most plastic resins, there will be no readily available way to bleed off or ground the static electricity which may be built up along the filler pipe itself.
It is also desirable that fuel filler pipes when made of plastic be capable of being joined to related structure. At one end this means connection to the tank. At the other end this conduit will be joined to a filler coupling. Such connection at one or both ends may be made by welding, particularly where two similar thermoplastic materials are involved. Such welding is commonly done by raising the temperature of the two surfaces to be joined and then bringing the two molten surfaces into contact to enable fusion to occur as cooling occurs.
Connections may also be required or desired at points along the conduit and it may be especially desirable that one or more of such connections are electrically connected to assist in bleeding off static electricity.
Thus, there is need for a fuel filler conduit which may be economically manufactured from plastic resins which inhibits the passage of vapours through the conduit to the surrounding atmosphere and which at the same time provides an electrically conductive path sufficient to prevent the build up of static electricity by fuel passing along the conduit.